The present invention relates to wireless communication systems and, more particularly, to a method and apparatus capable of effectively handling semi-persistent scheduling (SPS) of transmission resources.
The Long Term Evolution wireless communication system (LTE system), an advanced high-speed wireless communication system, supports only packet-switched transmission. The LTE system includes two scheduling methods: dynamic scheduling (DS) and semi-persistent scheduling (SPS). For DS, a network terminal dynamically allocates resources by transmitting control signaling on a physical downlink control channel (PDCCH) to user equipments (UEs). The resources, e.g., certain frequencies and time slots, allocated for data reception or transmission may vary according to requirements, such as traffic volume and quality of service (QoS). For SPS, in order to serve upper layer applications that generate semi-statically sized data periodically, e.g., voice over Internet protocol (VoIP) services, the network terminal allocates periodic semi-persistent resources to UEs. This reduces control signaling sent on a PDCCH and enhances system scheduling performance. Using SPS, the UE can periodically perform data transmission without receiving additional PDCCH signaling.
The resources assigned by DS are addressed to a cell radio network temporary identifier (C-RNTI) of the UE. The resources assigned by SPS are addressed to an SPS C-RNTI of the UE. The SPS C-RNTI is a specific UE identity assigned by the network terminal via a radio resource control (RRC) layer. The SPS C-RNTI is mainly used for configuring or reconfiguring an SPS resource and for indicating SPS retransmissions. In detail, when the UE has an assigned SPS C-RNTI, the UE needs to monitor its SPS C-RNTI on the PDCCH to determine subsequent operations according to a new data indicator (NDI) included in the PDCCH. If the value of the NDI is 0, it signals that the SPS resource needs to be configured or reconfigured. If the value of the NDI is 1, it signals SPS retransmission.
The 3rd Generation Partnership Project (3GPP) has started to specify a next generation of the LTE system: the LTE Advanced (LTE-A) system. Carrier aggregation (CA), for which two or more component carriers are aggregated, is included in into the LTE-A system to support wider transmission bandwidth, e.g., up to 100 MHz, and for spectrum aggregation. In other words, in the LTE-A system, a UE may utilize multiple subcarriers for data transmission with a network terminal to enhance transmission bandwidth and spectrum efficiency.
Using CA, after a UE establishes an RRC connection with a network terminal via a cell (which contains an uplink subcarrier and a downlink subcarrier), the network terminal can configure one or more downlink subcarriers to the UE via an RRC message, such that the UE can simultaneously utilize multiple subcarriers to perform data transmission. If the network terminal uses SPS, the UE may need to monitor PDCCHs of many downlink subcarriers to determine whether a semi-persistent resource is configured or reconfigured or an SPS retransmission is triggered. In such a situation, the more configured subcarriers, the more PDCCHs the UE needs to monitor. This may increase power consumption or SPS false alarm rates.